The present invention relates to a pneumatic radial tire, and more particularly, a pneumatic radial tire improved in or relating to the road noise generation without sacrifice to the resistance to the bead detachment from rim.
Road noise means noise generated inside a running car as a result of tires of the car contacting a roughened pavement surface. That is to say, that road noise generation is such a phenomenon in which when tires are caused to vibrate by delicate disturbances which they receive from a pavement surface, the vibration of the tires excites various portions of the car body to vibrate through suspension mechanisms of the car, whereby noise become generated inside the running car. Thus, in order to suppress the noise generation, it may be well devised to let the tires alleviate and/or absorb disturbances which they receive from the pavement surface so as to suppress to minimum the degree of transmission of vibration from tires to the car body.
Conventionally, as means for suppressing the transmission of vibration, it has been proposed to make use of a rubber having a large energy loss, namely a rubber having a large loss tangent, tan .delta., or to increase the volume of rubber, in the tread portion of the tire. However, according to such proposed means, the rolling resistance of the tire becomes disadvantageously increased and the fuel consumption economy is greatly sacrificed. Also, it has been proposed to dispose a soft rubber in a region below a bead core in the bead portion of the tire. According to this proposed measure, however, the resistance of the tire to the bead detachment from rim tends to be deteriorated and the tire tends to be unable to perform a stable running in a condition thereof having a lower inflation pressure than the prescribed normal value.
Then, if the pressure under which the tire fits to to a rim is increased in order to obtain a resistance to the bead detachment from the rim, it is necessary to apply a very high air pressure (internal pressure) to the tire at the time of mounting the tire on the rim, when a problem is likely that the tire and/or the rim may become impaired.